Chapter 10H e a t

Heat & Temperature

• Temperature is _____.– how hot or cold something is (a physical

property)– related to the average (kinetic) energy of the

substance (not the total energy)– Measured in units of

• Degrees Fahrenheit (oF)• Degrees Celsius (oC)• Kelvin (K)

Temperature Scales

• Fahrenheit Scale, °F– Water’s freezing point = 32°F, boiling point = 212°F

• Celsius Scale, °C– Temperature unit larger than the Fahrenheit– Water’s freezing point = 0°C, boiling point = 100°C

• Kelvin Scale, K– Temperature unit same size as Celsius– Water’s freezing point = 273 K, boiling point = 373 K

A b s o l u t e Z e r o

• T h e t e m p e r a t u r e a t w h i c h a l l m o l e c u l a r m o t i o n s t o p s . • T h e t e m p e r a t u r e

w o u l d b e z e r o K e l v i n s o r a b o u t

- 2 7 3 o C .

Temperature of ice water and boiling water.

Heat• Heat is the flow of energy due to a temperature

difference– Heat flows from higher temperature to lower

temperature• Heat is transferred due to “collisions” between

atoms/molecules of different kinetic energy• When produced by friction, heat is mechanical

energy that is irretrievably removed from a system

H e a t T r a n s f e r

• H e a t T r a n s f e rH e a t T r a n s f e r– C o n d u c t i o nC o n d u c t i o n– C o n v e c t i o nC o n v e c t i o n– R a d i a t i o nR a d i a t i o n

Conduction Through a Heated Rod

HOT(lots of vibration)

COLD(not much vibration)

Heat travelsalong the rod

Convection

Convection is heat transfer by bulk movement within a heated fluid such as a liquid or a gas. Free convection is caused by expansion of fluids when heated, causing hot regions to become buoyant. Circulation occurs as the hot fluid cools and sinks down again.Free convection systems can be very large and convey massive amounts of heat, for instance in weather systems and the circulation of molten rock inside the Earth.

Radiators make use of convection to transfer the heat from hot materials (water, night

storage bricks) to a room.

Specific Heat

Why do some foods stay hot longer than

others?

Why is the beach sand hot, but the water is

cool on the same hot day?

Heat (cont.)• The heat energy absorbed by an object is

proportional to:– The mass of the object (m)

– The change in temperature the object undergoes (T)

– Specific heat capacity (s) (a physical property unique to the substance)

• To calculate heat (Q):Q = c . m . T

Specific Heat

Different substances have different capacities for storing energyIt may take 20 minutes to heat water to 75°C. However, the same mass of aluminum might require 5 minutes and the same amount of copper may take only 2 minutes to reach the same temperature.

Specific Heat

Different substances have different capacities for storing energyIt may take 20 minutes to heat water to 75°C. However, the same mass of aluminum might require 5 minutes and the same amount of copper may take only 2 minutes to reach the same temperature.

Plates?

Plate

Review of Plate Tectonics

• What drives Earth processes?– gravity and density differences– external (e.g. hydrologic cycle, erosion)– internal (e.g. mantle convection)

Plate Boundaries

• divergent (constructive)• transform• convergent (destructive)

– ocean-ocean (e.g. Mariana Islands)– ocean-continent (e.g. Pacific-North America)– continent-continent (e.g. India-Asia)